Influence of cultivation systems and associated environmental factors on the growth performance of Hypnea musciformis seaweed at the south-east coast of the Bay of Bengal, Bangladesh

The production performance and interlinkages between environmental parameters and growth performances of Hypnea musciformis were evaluated under two cultivation techniques, namely "off-bottom long-line" and "off-bottom net", for a period of nine months from September 2021 to May 2022 at the Nuniachara regions of the south-east coast of the Bay of Bengal, Bangladesh. For this study, five off-bottom long-line (14 m x 5 m) and five off-bottom net (3.5 m x 3.5 m) cultivation plots were established and managed in a participatory farming approach with coastal communities. When growing to a length of 30-40 cm, H. musciformis was partially harvested every 15-30 days, depending on the cultivation months. The gross weight biomass (GWB) in the off-bottom net cultivation system was almost two folds higher than the off-bottom long-line system. Similarly, the average daily growth rate (DGR) was found to be 33% higher in the off-bottom net cultivation system compared to the off-bottom long-line system. The correlation analysis demonstrated that various environmental parameters were significantly correlated (p < 0.05) with the GWB and DGR of H. musciformis. Temperature, Turbidity, and Total Suspended Solids were significantly (p < 0.001) negatively correlated, while salinity and different nutrient concentrations (NO3-N, NO2-N, and PO4-P) were significantly (p < 0.001) positively correlated with the GWB and DGR of H. musciformis seaweed. Furthermore, multivariate principal component analysis (PCA) revealed that high concentrations of nutrients (NO3-N, NO2-N, and PO4-P) and salinity positively influenced the DGR and GWB from December to February, while the opposite ecological processes were responsible for the lower DGR and GWB values of H. musciformis in the other cultivation months. The findings of the present study demonstrated that the off-bottom net cultivation system could be a promising farming technology for producing carrageenan-enriched H. musciformis.